Dilated Cardiomyopathy in Dogs

Dilated Cardiomyopathy in Dogs
Patti S. Snyder, DVM, MS, DACVIM
Associate Professor, University of Florida

Dilated cardiomyopathy (DCM) is a very common form of heart disease in dogs. Only degenerative valve disease (also called mitral valve disease or endocardiosis or mitral insufficiency) and in some places heartworm disease are more common. It was not until the 1970s, when echocardiography began to be performed in veterinary institutions, that dilated cardiomyopathy could be diagnosed non-invasively with any certain degree of accuracy. The reported prevalence in dogs is approximately 0.5 percent.
Based upon a national database of dogs presented to veterinary schools in North America, we know that 5.8 percent of the Doberman Pinschers that were seen at a school had DCM, 5.6 percent of the Irish Wolfhounds presented had DCM. 3.9 percent of the Great Danes, 3.4 percent of the Boxers and 2.6 percent of the St. Bernards. The prevalence in purebred dogs in 0.65 percent whereas the prevalence in mixed breed dogs is 0.16 percent. In general, the dogs are middle age (4-10 years of age, with the exception of the Portuguese Water Dog (0.5 8 months)). Males are over-represented (2:1). Seventy to 80 percent of the Dobermans with congestive heart failure due to DCM are male and in a recent paper describing the disease in Dalmatians, all of the affected animals were male. This does not mean that female dogs are not affected by DCM, on the contrary, Dr. O’Grady at the University of Guelph found no sex predilection for Dobermans with subclinical (Asymptomatic or occult) DCM.
In most of the dogs that eventually die of DCM, the heart is very enlarged and appears flabby on examination. However, regardless of how symptomatic the dogs were before they died or how abnormal the heart looks upon gross inspection, the microscopic appearance of the heart is not often very dramatic. So the microscopic appearance belies the severity of the problem.
There are many proposed reasons for DCM including viral infection, toxins, nutrition, small blood vessel disease, genetic abnormalities, etc., but there is not likely to be one cause for the disease in all affected dogs.

Familial and Genetic Influences
The general feeling is that most cases of DCM have a familial or genetic basis. This is based upon the observation of a higher prevalence in purebred dogs, in certain breeds and within certain families. However, in only rare instances have the genetics for the disease been described. For example, Boxers with cardiac arrhythmias have an autosomal dominant trait.
There are also strong indications in other breeds such as the Doberman, where DCM can affect more than 50 percent of family members. In Portuguese Water Dogs DCM appears to be autosomal recessive and in English Cocker Spaniels it is associated with a particular immune deficit. An autosomal dominant mode of transmission has been proposed for the Newfoundlands with DCM.

Nutritional Influences
L-Carnitine L Carnitine deficiency has been identified in some dogs with dilated cardiomyopathy. Unfortunately we know from animal models that carnitine deficiency can be created by making the heart beat at very rapid heart rate (using a pacemaker); we also know that very rapid heart rates are common in dogs with DCM. Therefore the carnitine deficiency that was reported in earlier years may be the result of, rather than the cause of, DCM. So while we had all hoped that carnitine supplementation would resolve or prevent DCN in dogs, unfortunately it hasn’t. Many people choose to supplement L-carnitine in the diets of dogs with DCM and it is not likely to cause them any harm, but it is costly and may not be of any real benefit. Boxers with DCM should get 2-3 grams every 12 hours. If you want to supplement a Cocker Spaniel with DCM, the recommended dose is 1 gram of L-carnitine every 12 hours. DO NOT GIVE D-CARNITINE OF D,L-CARNITINE.

Taurine In the late 1980s taurine deficiency was recognized as the cause of dilated cardiomyopathy in the majority of cats with DCM. Since then investigators in the field have taken a close look for taurine deficiency in dogs with heart disease. In a study of dogs with DCM, 13 of 76 dogs had low taurine concentrations and this included three of three Cocker Spaniels with DCN and four of six Golden Retrievers with DCM. Dobermans on the other hand had normal taurine concentrations. When Cocker Spaniels (in a larger study) were supplemented with taurine and L-carnitine, in MOST but not all cases, their heart function improved. Subsequent to this report some people have stopped using the L-carnitine and still had success in improving heart function in some cases. Once blood is drawn for taurine evaluation, Cockers with DCM should get 500 mg TAURINE every 12 hours.

Very recently investigators in Scotland have determined that many Newfoundlands with DCM had low plasma taurine concentrations. At this point they have not described whether supplementation of these dogs resulted in any improvement of clinical signs.

CoEnzyme Q There have been several studies of the use of CoEnzyme Q in human patients but none have been published in the veterinary literature. Some of the studies in humans have shown some benefit while others have shown no benefit. It is not likely that a CoEnzyme Q deficiency is the CAUSE of DCM in dogs but it is an antioxidant and is not likely to be harmful to dogs with heart disease. Unfortunately it is expensive and since there is no proven benefit, it is hard to recommend an appropriate dose. The current doses that are reported are not based upon any scientific evidence.

Breed Specific Differences
Doberman Pinschers People have known about sudden cardiac death in Dobermans since the 1940s. Most of the early male dogs imported into the US to form our current breeding stock died suddenly, most likely due to DCM.
DCM in Dobermans is manifested in several ways. The dogs may have arrhythmias or congestive heart failure as their primary presenting problem. Either of these may lead to death of the dog (arrhythmias (ventricular tachycardia, VPCs) are common in Dobermans who develop symptoms for dilated cardiomyopathy. These arrhythmias are found in virtually 100 percent of the Dobermans that die from DCM. These arrhythmias can also be seen in dogs that are not symptomatic for DCM at the time (but these dogs often later on develop DCM). In one study, about 13 percent of Asymptomatic Dobermans had arrhythmias on an electrocardiogram.
Because of the high prevalence of this disease in Dobermans, several investigators have evaluated Dobermans who are not symptomatic in an attempt to define the early stages of the disease. Many of the Dobermans examined that did not have any symptoms of heart disease (e.g. the subclinical symptoms), were in fact found to have heart dysfunction. Despite these subclinical dogs not having symptoms at the time of their initial examination, 30 percent went on to develop heart failure or died suddenly, presumably due to arrhythmias. Based on this study, echocardiographic criteria have been developed to help identify Dobermans that are at substantial risk for developing symptoms. These criteria are:
The internal diameter of the left ventricle during relaxation (LVIDD) > 46 mm
The internal diameter of the left ventricle during contraction (LVIDS) > 38 mm
The current thought is that DCM is a slowly progressive disease in Dobermans that worsens over a period of two to four years eventually leading to more severe arrhythmias and in many cases, congestive heart failure. Once the dogs become symptomatic, standard therapies for treatment of the heart failure and/or cardiac arrhythmias should be instituted.
Nonetheless, the prognosis for Dobermans with DCM is poor. One study reported the average survival time is approximately three months once clinical signs of heart failure are seen. Another study reported the average survival time of 2.4 months.

Boxer Cardiomyopathy in Boxers was first described by Dr. Neil Harpster in the early 1980s. He defined three types. Type I was the Boxer with arrhythmias that was not symptomatic. Type II was the Boxer that had arrhythmias that was symptomatic (usually collapse) and Type III was the Boxer with congestive heart failure that may also have arrhythmias. Since then numerous Boxers have been evaluated for the disease and we now recognize that most of the Boxers fit into either the Type I or Type II categories. This has prompted some people to call the disease Boxer Arrhythmia Disease or Boxer Dysrhythmia rather than dilated cardiomyopathy. Cardiac arrhythmias (ventricular tachycardia, VPCs) are the common arrhythmia seen in the Boxers with DCM.
The disease in Boxers is now known to be an autosomal dominant trait with variable penetrance3. Most of the dogs on initial examination will have a normal physical examination but in some cases an arrhythmia is detected and in rare cases a murmur is heard. Most of the dogs (~ 90 percent) will have a normal echocardiogram (hence the reason for the suggested name change).
Holter monitoring (continuous ambulatory electrocardiography) is the good method to examine Boxers for the disease. Since we know normal dogs rarely have ventricular arrhythmias, finding of frequent arrhythmias suggest cardiac disease. What we do not know at this point is whether the information about the frequency or rate of arrhythmia we observe on the Holter recording will help establish an idea of severity or prognosis.

Irish Wolfhound Ventricular arrhythmias are not common in the Irish Wolfhound however arrhythmias originating higher up in the atria are common (atrial fibrillation). This is seen in up to 80 percent of the Irish Wolfhounds with DCM.
In a large study in Germany, 500 Irish Wolfhounds were examined. Abnormal cardiac findings were seen in 42 percent (n=209) of the dogs. Dilated cardiomyopathy was diagnosed in 24 percent (n=121) and was subclinical in about half these. Atrial fibrillation was present in 88 percent of the dogs with DCM. The median survival time was 5.1 months.

Cocker Spaniel Both English and American Cocker Spaniels have been reported to develop DCM. Some of them have low plasma taurine concentrations and show improvement with taurine supplementation (as well as other standardized treatment for heart failure). All Cocker Spaniels with DCM should have plasma taurine concentrations evaluated and while waiting for results the dogs should be supplemented. In some but not all cases, the other cardiac medications can eventually be discontinued.
In one breeding of English Cocker Spaniels there was a strong association between the DCM and a particular immune defect (C4 phenotype).
In a study where American Cockers with DCM that were supplemented with taurine and carnitine, dogs < ten years of age lived an average of 46 + eleven months whereas dogs > ten years of age lived an average of 14 + seven months.

Portuguese Water Dog There has been a report of twelve related Portuguese Water Dogs with DCM. What is unique in this case is that the dogs were young (average thirteen weeks). The dogs died quickly of congestive heart failure. An autosomal recessive pattern of inheritance is suspected.

Dalmatians All nine of the affected dogs in one study were male with an average age of 6.8 years. Eight of the nine dogs had been fed a low protein diet to prevent bladder stones.
The presentation of the dogs was classic for congestive heart failure and the median survival was ten months. Three of the dogs were supplemented with carnitine without any substantial improvement. Four dogs were tested for taurine deficiency and all were normal. Six of the nine dogs were taken off the protein restricted diet; one improved. The report does not state the eventual outcome of this dog.

Great Danes Great Danes with dilated cardiomyopathy often present in congestive heart failure, with or without cardiac arrhythmias. Like the Irish Wolfhound, atrial fibrillation is the most common arrhythmia seen in Great Danes with DCM. Based on recent pedigree analysis, DCM in this breed is believed to be an X-linked recessive trait. So affected dogs should not be bred and males borne to affected females are at increased risk of developing DCM.

Clinical Signs:
NONE
Fainting (Dobermans, Boxers)
Difficulty breathing
Coughing
Distended abdomen (Ascites)
Weight loss
Cold extremities and ears
Weakness and exercise intolerance
Sudden, unexpected death

Treatment
Treatment of dilated cardiomyopathy is quite variable and depends upon the severity of the problem as well as the predominating symptom (e.g. fainting vs. coughing). The treatment may include things such as a moderately sodium restricted diet, diuretics (such as Lasix®), digoxin, nitroglycerin, ACE inhibitors (such as Enacard®, Vasotec®, Lotensin®) and various antiarrhythmic agents (such as lidocaine, procainamide, sotalol, quinidine). Taurine and carnitine may also be added.

HEART CERTIFICATION by the Orthopedic Foundation for Animals:
Heart certification by OFA is aimed at gathering data regarding congenital heart disease. They state on their website:

At this time the inherited, developmental cardiac diseases like subaortic stenosis and cardiomyopathies (emphasis added) are difficult to monitor since there apparently is no clear cut distinction between normal and abnormal. The OFA will modify the congenital cardiac database when a proven (echocardiography/Holter) diagnostic modality and normal parameters by breed are established.

Dog Owners and Breeders Symposium
July 28, 2001
University of Florida
College of Veterinary Medicine

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